Method for recycling waste plastic into concrete

ABSTRACT

A method of making a structural lightweight and thermal insulating concrete is described. The concrete has a coarse aggregate partly replaced by recycled plastic pieces. This enables the concrete to maintain a high compressive strength, low thermal conductivity, and low weight, while providing a use for waste plastic. The waste plastic pieces may comprise polyethylene in the form of flakes, fibers, or granules. Due to its low unit weight, adequate compressive strength and high thermal resistance the developed concrete can be used as a structural lightweight and thermal insulating concrete. The use of this concrete leads to economic and environmental benefits.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of Ser. No. 16/026,734, nowallowed, having a filing date of Jul. 3, 2018 which claims benefit ofpriority to U.S. Provisional Application No. 62/666,133 having a filingdate of May 3, 2018 which is incorporated herein by reference in itsentirety.

STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTORS

Aspects of this technology were described in an M.S. thesis presentationgiven by Shaik Inayath Basha on May 16, 2017 at the Department of Civiland Environmental Engineering at King Fand University of Petroleum &Minerals in Dhahran, Saudi Arabia, with the title of “Development ofLight Weight, Thermal Resistant Concrete Utilizing Recycled PlasticAggregates,” and is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a composition for making a structurallightweight and thermal insulating concrete having a portion of thecoarse aggregates replaced with waste plastic particles.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Lightweight concrete (LWC) is a conglomerate of cement and lightweightaggregates. It has a bulk density in the range of 300 to 2,000 kg/m³compared to a value of 2,200 to 2,600 kg/m³ of normal weight concrete(NWC). Some of the advantages of LWC include: (i) reduction in the deadload, and (ii) lighter and smaller elements. LWC that can be used toproduce structural members is called structural lightweight concrete(SLWC)

According to ACI 213, SLWC is a concrete that is prepared withlightweight aggregates and whose average unit weight ranges between1,400 to 2,000 kg/m³, and it has a compressive strength of more than20.0 N/mm². SLWC provides technical, environmental, and economicadvantages, and is on the way to become a material of the future, withthe world growing more conscious of energy conservation andenvironmental protection.

There are clear advantages of SLWC over NWC. SLWC has a greaterstrength/weight ratio, lower thermal conductivity, superiorfire-resistance, and better durability. The use of SLWC decreases theweight of a structural member, which leads to a reduction in the sizesof columns, beams, walls, and foundations and therefore reduces theresulting seismic loads and earthquake damage. However, the mostsignificant potential advantage of SLWC is the environmental protection,particularly, if the raw materials needed for the production of SLWC arederived from waste products. While several materials have been used inthe production of SLWC, there is a need to beneficially utilize recycledplastic in concrete. Such a use will lead to technical and economicadvantages and also results in environmental benefits by finding a usefor non-biodegradable waste plastic.

Over 300 million metric tons of plastic are consumed globally per year,and it has grown over the last five years at an estimated rate of 3.4%annually. The exponential growth in population, urbanization, trade, andindustry is not only accelerating plastic consumption but alsoincreasing the production rate of all classes of waste plastics.

The accumulation of huge volumes of commodity waste plastics derivedfrom municipal solid waste and other household items has become a majorwaste management issue over the past two decades. The threat of plasticwaste seems to be always growing as it is non-biodegradable and may leadto contamination of soil, air and water, as shown in FIGS. 1A-IF.

In the plastic waste stream, polyethylene (HDPE & LDPE) forms thelargest fraction, followed by PET, PP, and PS. The earlier trends, suchas land filling and incineration of these non-biodegradable materialscreate substantial air pollution, and in the long-run a worldwide threatto the environment and public health.

Recovery and recycling, however, remain insufficient, and millions oftons of plastics end up in landfills and oceans each year. Themechanical recycling of the plastic waste and its utilization inconcrete or mortar preparation appears as one solution for disposing theused plastics, because of economic and environmental benefits.

In view of the forgoing, one objective of the present invention is toprovide a method of making a lightweight structural concrete with highthermal insulation. Recycled plastic is utilized as a coarse aggregate.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present disclosure relates to a methodof making a structural lightweight concrete. This first involves mixing12-25 wt % Portland cement, 37-57 wt % fine aggregate, 5-40 wt % coarseaggregate, and 5-12 wt % water to form a wet concrete slurry, whereineach weight percentage is relative to a total weight of the wet concreteslurry. Then the wet concrete slurry is cured to produce the structurallightweight concrete. The coarse aggregate comprises 10-100 wt % wasteplastic pieces, relative to a total weight of the coarse aggregate, andthese waste plastic pieces have an average longest dimension of 1-12 mm.

In one embodiment, the waste plastic pieces are in the form of granules,fibers, and/or flakes.

In a further embodiment, the waste plastic pieces are in the form ofgranules having a cylindrical shape with an average diameter of 1-4 mmand an average length of 1-7 mm.

In a further embodiment, the waste plastic pieces are in the form offlakes having an average thickness of 0.3-0.8 mm and an average longestdimension of 1-8 mm.

In a further embodiment, the waste plastic pieces are in the form offibers having an average diameter of 0.2-0.8 mm and an average length of2-12 mm.

In one embodiment, the waste plastic pieces have a specific gravity of0.80-1.20.

In one embodiment, the waste plastic pieces have a surface roughness Raof 1-50 μm.

In one embodiment, the method further comprises reshaping the wasteplastic pieces by melting, extruding, or grinding.

In one embodiment, the waste plastic pieces comprise 20-100 wt %polyethylene, relative to a total weight of the weight plastic pieces.

In one embodiment, the wet concrete slurry further comprises 0.1-2.0 wt% of a superplasticizer relative to a total weight of the wet concreteslurry.

In one embodiment, the superplasticizer is a polycarboxylate ether.

In a further embodiment, where the superplasticizer is a polycarboxylateether, the wet concrete slurry has a slump of 50-150 mm.

In one embodiment, the Portland cement is an ASTM C 150 cement selectedfrom the group consisting of Type I, Type Ia, Type II, Type IIa, TypeII(MH), Type II(MH)a, Type III, Type IIIa, and Type IV.

In one embodiment, the fine aggregate is sand with an average particlesize of less than 1.5 mm.

In one embodiment, the coarse aggregate further comprises at least oneselected from the group consisting of limestone, perlite, and scoria, ata weight percentage of 1-90 wt % relative to a total weight of thecoarse aggregate.

In a further embodiment, limestone is present, having an averageparticle size of 1-20 mm.

In one embodiment, the structural lightweight concrete has a compressivestrength of 20-40 MPa.

In one embodiment, the structural lightweight concrete has a thermalconductivity of 0.50-1.10 W/(m·K).

In one embodiment, the structural lightweight concrete has a unit weightof 1,400-2,000 kg/m³.

In one embodiment, the structural lightweight concrete does not comprisefly ash.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1A is an image of waste plastic obstructing and polluting awaterway.

FIG. 1B is an image of tons of waste plastic stacked at a disposal site.

FIG. 1C is an image of plastic waste dumped in a dumping yard.

FIG. 1D is an image of waste plastic bottles floating on a body ofwater.

FIG. 1E is an image of cows eating plastic waste.

FIG. 1F is an image of a seal trapped in a plastic net.

FIG. 2A is an image of granule-shaped recycled plastic.

FIG. 2B is an image of fiber-shaped recycled plastic.

FIG. 2C is an image of white flake-shaped recycled plastic.

FIG. 2D is an image of black flake-shaped recycled plastic.

FIG. 3 is a graph showing the unit weights of SLWTIC specimenscomprising different amounts of granule-shaped recycled plastics as acoarse aggregate.

FIG. 4 is a graph of the compressive strengths of the SLWTIC specimensof FIG. 3.

FIG. 5 is a graph showing the thermal conductivities of the SLWTICspecimens of FIG. 3.

FIG. 6 is a graph showing the unit weights of SLWTIC specimenscomprising different amounts of fiber-shaped recycled plastics as acoarse aggregate.

FIG. 7 is a graph of the compressive strengths of the SLWTIC specimensof FIG. 6.

FIG. 8 is a graph showing the thermal conductivities of the SLWTICspecimens of FIG. 6.

FIG. 9 is a graph showing the unit weights of SLWTIC specimenscomprising different amounts of fiber-shaped recycled plastics as acoarse aggregate.

FIG. 10 is a graph of the compressive strengths of the SLWTIC specimensof FIG. 9.

FIG. 11 is a graph showing the thermal conductivities of the SLWTICspecimens of FIG. 9.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure will now be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all embodiments of the disclosure are shown.

The present disclosure will be better understood with reference to thefollowing definitions. As used herein, the words “a” and “an” and thelike carry the meaning of “one or more.” Within the description of thisdisclosure, where a numerical limit or range is stated, the endpointsare included unless stated otherwise. It will be further understood thatthe terms “comprises” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

As used herein, the words “about,” “approximately,” or “substantiallysimilar” may be used when describing magnitude and/or position toindicate that the value and/or position described is within a reasonableexpected range of values and/or positions. For example, a numeric valuemay have a value that is +/−0.1% of the stated value (or range ofvalues), +/−1% of the stated value (or range of values), +/−2% of thestated value (or range of values), +/−5% of the stated value (or rangeof values), +/−10% of the stated value (or range of values), +/−15% ofthe stated value (or range of values), or +/−20% of the stated value (orrange of values). Within the description of this disclosure, where anumerical limit or range is stated, the endpoints are included unlessstated otherwise. Also, all values and subranges within a numericallimit or range are specifically included as if explicitly written out.

As used herein, “compound” is intended to refer to a chemical entity,whether as a solid, liquid, or gas, and whether in a crude mixture orisolated and purified.

As used herein, “composite” refers to a combination of two or moredistinct constituent materials into one. The individual components, onan atomic level, remain separate and distinct within the finishedstructure. The materials may have different physical or chemicalproperties, that when combined, produce a material with characteristicsdifferent from the original components. In some embodiments, a compositemay have at least two constituent materials that comprise the sameempirical formula but are distinguished by different densities, crystalphases, or a lack of a crystal phase (i.e. an amorphous phase). As usedherein, specific gravity is the ratio of the density of a substance tothe density of a reference substance; equivalently, it is the ratio ofthe mass of a substance to the mass of a reference substance for thesame given volume. Apparent specific gravity is the ratio of the weightof a volume of the substance to the weight of an equal volume of thereference substance. As used herein, the reference substance is water ata temperature 2-25° C., preferably 4-22° C. and a pressure ofapproximately 1 atm (˜101 kPa).

According to a first aspect, the present disclosure relates to a methodof making a structural lightweight concrete (SLWC). This method involvesmixing Portland cement, fine aggregate, coarse aggregate, and water toform a wet concrete slurry. The wet concrete slurry is cured to producethe structural lightweight concrete.

As used herein, “structural lightweight concrete” also includesaggregate that is either entirely lightweight aggregate or a combinationof lightweight and normal density aggregate. As used herein,“lightweight aggregate” as defined in ASTM C 330 has a bulk density ofless than 1120 kg/m³ (70 lb/ft³) for fine aggregate and less than 880kg/m³ (55 lb/ft³) for coarse aggregate. As used herein, the terms “fine”and “coarse” refer to the average particle size, here the averageparticle size of the aggregate and additives of the structurallightweight concrete. As used herein, average particle size refers tothe longest linear dimension of the particle. In terms of the presentdisclosure, “coarse” may refer to having an average particle size ofgreater than 1.5 mm, preferably greater than 5 mm, preferably greaterthan 10 mm, while “fine” may refer to having an average particle size of1.5 mm or less, preferably 1.0 mm or less.

“Structural lightweight concrete” is further defined in ASTM C 330 asconcrete having a minimum 28-day compressive strength of 17 MPa (2500psi) and an equilibrium density in the range of 1120-1920 kg/m³ (70-120lb/ft³). This stands in contrast to normal weight concrete. As usedherein, “normal weight concrete” refers to concrete having anequilibrium density of 2240-2480 kg/m³ (140-155 lb/ft³). This definitionis not a specification, project specifications vary by necessity. Whilestructural lightweight concrete with an equilibrium density of 1120-1680kg/m³ (70-105 lb/ft³) is infrequently used, most structural lightweightconcrete has an equilibrium density of 1680-1920 kg/m³ (105-120 lb/ft³).As used herein, “equilibrium density” as defined in ASTM 567 is thedensity reached by structural lightweight concrete after exposure torelative humidity of 50±5% and a temperature of 23±2° C. for a period oftime sufficient to reach a density that changes less than 0.5% in aperiod of 28 days.

In a preferred embodiment, the cement of the lightweight concretecomposition of the present disclosure is a hydraulic cement, preferablya sulfoaluminous clinker, preferably Portland cement. As used herein,“Portland cement” refers to the most common type of cement in generaluse around the world developed from types of hydraulic lime and usuallyoriginating from limestone. It is a fine powder produced by heatingmaterials in a kiln to form what is called clinker, grinding theclinker, and adding small amounts of other materials. The Portlandcement is made by heating limestone (calcium carbonate) with othermaterials (such as clay) to >1400° C. in a kiln, in a process known ascalcination, whereby a molecule of carbon dioxide is liberated from thecalcium carbonate to form calcium oxide, or quicklime, which is thenblended with the other materials that have been included in the mix tofrom calcium silicates and other cementitious compounds. The resultinghard substance, called “clinker” is then ground with a small amount ofgypsum into a powder to make ordinary Portland cement (OPC). Severaltypes of Portland cement are available with the most common being calledordinary Portland cement (OPC) which is grey in color. The low cost andwidespread availability of the limestone, shales, and other naturallyoccurring materials used in Portland cement make it one of the low costmaterials widely used throughout the world. However, Portland cement iscaustic, can contain some hazardous components and carries environmentalconcerns such as the high energy consumption required to mine,manufacture, and transport the cement and the related air pollutionincluding the release of greenhouse gases, dioxins, NO_(x), SO₂, andparticulates.

Clinkers make up approximately 90% of Portland cement along with alimited amount of calcium sulfate (which controls the set time) and upto approximately 5% minor constituents (i.e. filler) as allowed byvarious standards. In a preferred embodiment, clinkers are nodules withan average particle diameter of approximately 2-30 mm, preferably 5-25mm, preferably 8-20 mm of a sintered material that is produced when araw mixture of predetermined composition is heated to high temperature.The key chemical reaction which defines Portland cement from otherhydraulic limes occurs at these temperatures (>1200° C.) and is whenbelite (Ca₂SiO₄) combines with calcium oxide (CaO) to form alite(Ca₃SiO₅).

Portland cement clinkers are generally made by heating (i.e. in a cementkiln) a mixture of raw materials to a calcining temperature of above500° C. and then a fusion temperature, which is approximately 1400° C.for modern Portland cements to sinter the materials into clinker. Thematerials in Portland cement clinker are alite, belite, tricalciumaluminate, and tetracalcium alumino ferrite. The aluminum, iron, andmagnesium oxides are present as a flux allowing the calcium silicates toform at a lower temperature and do not generally contribute to strength.For specific Portland cements (i.e. low heat or sulfate resistant types)it may be necessary to limit the amount of tircalcium aluminate(3CaO.Al₂O₃) that is formed. The major raw material for the clinkermaking process is usually limestone (CaCO₃) mixed with a second materialcontaining clay as source of alumino silicate. Often, an impurelimestone which contains clay or SiO₂ is used. The CaCO₃ content ofthese limestones can be as low as 80%. Secondary raw materials(materials in the raw mix other than limestone) depend on the purity ofthe limestone. Secondary raw materials may include, but are not limitedto, clay, shale, sand, iron ore, bauxite, fly ash, slag and the like,when a cement kiln is fired by coal, the ash of the coal may act as asecondary raw material.

Often to achieve the desired setting qualities in the finished Portlandcement product, a quantity (˜1-10 wt %, preferably 2-8 wt %, or about 5wt %) of calcium sulfate (often in the form of gypsum or anhydrite) isadded to the clinker and the mixture is finely ground to form thefinished cement powder, such as for example in a cement mill. Thegrinding process may be controlled to obtain a powder having a broadparticle size range, in which typically 15% by mass consists ofparticles below 5 μm in diameter, and 5% by mass consists of particlesabove 45 μm in diameter. The measure of fineness most closely associatedwith cement is the specific surface area, which refers to the totalparticle surface area of a unit mass of the cement. The rate of initialreaction (˜ up to 24 hours) of the cement on addition of water isdirectly proportional to the specific surface area. In a preferredembodiment, the structural lightweight concrete of the presentdisclosure comprises cement having a specific surface area in the rangeof 250-450 m²·kg⁻¹, preferably 275-425 m²·kg⁻¹, preferably 300-400m²·kg⁻¹, preferably 320-380 m²·kg⁻¹. Typically, general purpose Portlandcement falls within these ranges, although it may be as high as 450-700m²·kg⁻¹ for “rapid hardening” cements.

As used herein, “Portland cement” or “Portland cement clinker” has atricalcium silicate ((CaO)₃.SiO₂, C₃S) content of 45-75 wt % relative tothe total weight of the cement, a dicalcium silicate ((CaO)₃.SiO₂, C₂S)content of 7-32 wt % relative to the total weight of the cement, atricalcium aluminate ((CaO)₃.Al₂O₃, C₃A) content of 0-13 wt % relativeto the total weight of the cement, a tetracalcium aluminoferrite((CaO)₄.Al₂O₃.Fe₂O₃, C₄AF) content of 0-18 wt % relative to the totalweight of the cement, and a gypsum (CaSO₄.2H₂O) content of 0-10 wt %relative to the total weight of the cement. Furthermore, as used herein“Portland cement or “Portland cement clinker” has a calcium oxide (CaO,C) content of 61-67 wt % relative to the total weight of the cement, asilicon dioxide (SiO₂, S) content of 19-23 wt % relative to the totalweight of the cement, an aluminum oxide (Al₂O₃, A) content of 2.5-6 wt %relative to the total weight of the cement, a ferric oxide (Fe₂O₃, F)content of 0-6 wt % relative to the total weight of the cement, and asulfate (S) content of 1.5-4.5 wt % relative to the total weight of thecement.

The wet concrete slurry comprises Portland cement at a weight percentageof 12-25 wt %, preferably 15-22 wt %, more preferably 16-20 wt %, orabout 17 wt % or 19 wt %, relative to a total weight of the wet concreteslurry. However, in some embodiments, the wet concrete slurry maycomprise less than 12 wt % or greater than 25 wt % Portland cement. Inone embodiment, the Portland cement is an ASTM C 150 cement selectedfrom the group consisting of Type I, Type Ia, Type II, Type IIa, TypeII(MH), Type II(MH)a, Type III, Type Ma, and Type IV. Preferably thePortland cement is an ASTM C150 Type I cement, and may have acomposition similar to that shown in Table 1. In other embodiments, adifferent type of Portland cement may be used, or a blend of Portlandcement and another cement such as EN 197-1 CEM I, CEM II, CEM III, CEMIV, CEM V; or CSA A3000-08 GU, GUL, MS, MH, MHL, HE, HEL, LH, LHL, HS;white Portland cement, Portland blast furnace slag cement (or blastfurnace cement), Portland fly ash cement, Portland pozzolan cement,Portland silica fume cement, masonry cements, expansive cements, whiteblended cements, colored cements, very finely ground cements, pozzolanlime cements, slag lime cements, supersulfated cements, calciumsulfoaluminate cements, “natural” cements and geopolymer cements, andthe like and mixtures thereof. The Portland cement may have a specificgravity of 2.0-4.0, preferably 2.5-3.5, preferably 2.75-3.4, preferably3.0-3.3, preferably 3.1-3.2, or about 3.15. In one embodiment, thecement content in a mixture of the dry ingredients may be 300-400 kg/m³,preferably 320-380 kg/m³, or about 350 kg/m³ or 370 kg/m³.

The wet concrete slurry also comprises aggregates. As used herein,“construction aggregate” or simply “aggregate” refers to a broadcategory of particulate material used in construction. Exemplarymaterials include, but are not limited to, sand, gravel, crushed stone,slag, recycled concrete, geosynthetic aggregates, and the like.Aggregates are a component of composite materials, such as concrete; theaggregates serve as reinforcement to add strength to the overallcomposite material. The ASTM publishes a listing of specificationsincluding, but not limited to, ASTM D 692 and ASTM D 1073 for variousconstruction aggregate products, which by their individual design aresuitable for specific construction purposes. The products includespecific types of coarse and fine aggregate designed for such uses asadditives to concrete mixes. Fine and coarse aggregates make up the bulkof a concrete mixture. Sand, natural gravel, and crushed stone are usedmainly for this purpose. Recycled aggregates (from construction,demolition, and excavation waste) are increasingly used as partialreplacements for natural aggregates, while a number of manufacturedaggregates, including air-cooled blast furnace slag and bottom ash alsofind use. The presence of aggregate greatly increases the durability ofconcrete above that of cement, which is a brittle material in its purestate, reduces cost, and controls cracking caused by temperaturechanges. Thus, concrete is a true composite material. Sources of thesebasic materials can be grouped into three main areas: mining of mineralaggregate deposits (i.e. sand, gravel and stone), the use of waste slagfrom the manufacture of iron, steel and petroleum products or recyclingof concrete (itself chiefly manufactured from mineral aggregates), andobtaining some materials that are used as specialty lightweightaggregates (i.e. clay, pumice, perlite, vermiculite).

Aggregates, from different sources, or produced by different methods,may differ considerably in particle shape, size, and texture. The shapesof the aggregates of the present disclosure may be cubical andreasonably regular, essentially rounded, or angular and irregular.Surface texture may range from relatively smooth with small exposedpores to irregular with small to large exposed pores. Particle shape andsurface texture of both fine and coarse aggregates influenceproportioning of mixtures in such factors as workability, pumpability,fine-to-coarse aggregate ratio, cement binder content, and waterrequirement.

The wet concrete slurry comprises the fine aggregate at a weightpercentage of 37-57 wt %, preferably 40-55 wt %, more preferably 42-47wt %, even more preferably 44-45 wt %, relative to a total weight of thewet concrete slurry. However, in some embodiments, the fine aggregatemay be present at a weight percentage of less than 37 wt % or greaterthan 57 wt %. In one embodiment, the fine aggregate is sand, such asdesert sand or dune sand, with an average particle size of less than 1.5mm. In one embodiment, the fine aggregate may have an average particlesize of 0.1-5 mm, preferably 0.2-2 mm, more preferably 0.3-1.5 mm, evenmore preferably 0.4-1.0 mm. In an alternative embodiment, a fineaggregate may not be present in the wet cement slurry or in a curedconcrete composition. The fine aggregate may have a specific gravity of1.5-3.25, preferably 1.75-3.0, preferably 2.0-2.8, preferably 2.25-2.6.As used herein, water absorption refers to the penetration of water intoaggregate particles with resulting increase in particle weight. In oneembodiment, the fine aggregate has a water absorption of 0.1-1.0%,preferably 0.2-0.8%, preferably 0.4-0.6%, or about 0.5%.

As mentioned previously, the fine aggregate is sand, preferably dunesand. As used herein, “sand” refers to a naturally occurring granularmaterial composed of finely divided rock and mineral particles. It isdefined by size in being finer than gravel and coarser than silt. Thecomposition of sand varies, depending on the local rock sources andconditions, but the most common constituent of sand is silica (silicondioxide, or SiO₂), usually in the form of quartz. The second most commontype of sand is calcium carbonate, for example aragonite. In terms ofthe present disclosure, the fine aggregate of the concrete compositionmay be silicon dioxide sand, preferably quarzitic silicon dioxide,preferably quarzitic sand, preferably dune sand.

In terms of particle size, sand particles range in diameter from 0.0625mm to 2 mm. An individual particle in this range is termed a sand grain.By definition sand grains are between gravel (particles ranging from 2mm to 64 mm) and silt (particles ranging from 0.004 mm to 0.0625 mm).ISO 14688 grades sands as fines, medium and coarse with ranges of 0.063mm to 0.2 mm to 0.63 mm to 2.0 mm. Sand is also commonly divided intofive subcategories based on size: very fine sand (0.0625-0.125 mmdiameter), fine sand (0.125-0.250 mm diameter), medium sand (0.250-0.500mm diameter), coarse sand (0.500-1.0 mm diameter) and very coarse sand(1.0-2.0 mm diameter). These categories of based on the Krumbein phiscale, where size in ϕ=−log₂D; wherein D is the particle size in mm. Onthis scale, for sand the value of ϕ varies from −1 to +4, with thedivisions. In terms of the present disclosure, the fine aggregate of thewet concrete slurry may be sand, and may be very fine sand, fine sand,medium sand, or even coarse sand, preferably very fine sand, fine sandor medium sand.

In one embodiment, the fine aggregate is sand with an average particlesize of less than 700 μm, preferably less than 600 μm, preferably lessthan 500 μm, preferably less than 400 μm, preferably less than 300 μm,preferably less than 200 μm, preferably less than 100 μm, such as forexample 500-700 μm, preferably 525-675 μm, preferably 550-650 μm,preferably 575-625 μm. As used herein, the coefficient of variation orrelative standard deviation is expressed as a percentage and defined asthe ratio of the particle size standard deviation (σ) to the particlesize mean (μ) multiplied by 100. In a preferred embodiment, the fineaggregate of the concrete composition is sand having a coefficient ofvariation of less than 35%, preferably less than 30%, preferably lessthan 25%, preferably less than 20%, preferably less than 15%, preferablyless than 10%. In a preferred embodiment, the fine aggregate of theconcrete composition is sand having a particle size distribution rangingfrom 10% of the average particle size to 200% of the average particlesize, preferably 50-150%, preferably 75-125%, preferably 80-120%,preferably 90-110%.

In one embodiment, the sand comprises 80-95 wt % of silicon dioxide(SiO₂ or silica) relative to the total weight of the sand, preferably85-94 wt %, preferably 88-93 wt %, preferably 90-92 wt % of SiO₂relative to the total weight of the sand. The most common constituent ofsand is silicon dioxide (SiO₂ or silica), usually in the form of quartz,which due to its chemical inertness and considerable hardness, is themost common mineral resistant to weathering. In a preferred embodiment,the wet concrete slurry of the present disclosure comprises sand as fineaggregate and the sand further comprises ferric oxide (Fe₂O₃), aluminumoxide (Al₂O₃), magnesium oxide (MgO), and potassium oxide (K₂O). Thesecompounds are generally present in less than 5 wt % relative to thetotal weight of the sand, preferably less than 4 wt %, preferably lessthan 3 wt %, such as, for example, 0.1-2.0 wt %, preferably 0.2-1.0 wt%, preferably 0.4-0.9 wt % relative to the total weight of the sand.Other impurities may be present in the sand including, but not limitedto limestone, gypsum, sand stone, feldspar, granite, magnetite,chlorite, glauconite, basalts, iron, obsidian and the like or mixturesthereof.

In one embodiment, the wet cement slurry may comprise other fineaggregates. Exemplary suitable fine aggregates that may be used inaddition to, or in lieu of sand or dune sand include, but are notlimited to, mineral particles of natural or synthetic origin, pumice,expanded clays, expanded schists, expanded glasses, expanded aggregatesbased on marble, granite, slate, ceramic, and the like and mixturesthereof.

The wet concrete slurry of the present disclosure also comprises acoarse aggregate. In one embodiment, the coarse aggregate may have anaverage specific gravity of 0.2-2.8, preferably 0.3-2.6, preferably0.5-2.2, preferably 0.8-2.0, preferably 1.2-1.8, preferably 1.4-1.6. Ina preferred embodiment, wet concrete slurry comprises the coarseaggregate at a weight percentage of 5-40 wt %, preferably 10-35 wt %,more preferably 15-32 wt %, even more preferably 20-30 wt % relative toa total weight percent of the wet concrete slurry.

In one embodiment, the coarse aggregate comprises 10-100 wt % wasteplastic pieces, preferably 20-90 wt %, more preferably 22-60 wt %, evenmore preferably about 25 wt % or about 50 wt % relative to a totalweight of the coarse aggregate. In one embodiment, the coarse aggregatecomprises 100 wt % waste plastic pieces, meaning that no other coarseaggregate is present.

In one embodiment, the waste plastic pieces comprise 20-100 wt %,preferably 40-100 wt %, more preferably 60-100 wt %, even morepreferably 80-100 wt % polyethylene, relative to a total weight of theweight plastic pieces.

In one embodiment, the polyethylene may be ultra-high-molecular-weightpolyethylene (UHMWPE), ultra-low-molecular-weight polyethylene (ULMWPEor PE-WAX), high-molecular-weight polyethylene (HMWPE), high-densitypolyethylene (HDPE), high-density cross-linked polyethylene (HDXLPE),cross-linked polyethylene (PEX or XLPE), medium-density polyethylene(MDPE), linear low-density polyethylene (LLDPE) low-density polyethylene(LDPE), very-low-density polyethylene (VLDPE), chlorinated polyethylene(CPE), or mixtures thereof. Preferably the polyethylene is HDPE or LDPE.

In one embodiment, the polyethylene of the present disclosure has anaverage molecular weight of 2-300 kDa, preferably 5-200 kDa, preferably10-150 kDa, preferably 10-75 kDa, preferably 15-50 kDa, preferably 20-40kDa. The degree of polymerization (DP) is defined as the number ofmonomeric units in a macromolecule or polymer. In one embodiment, thepolyethylene of the present disclosure has a degree of polymerization inthe range of 100-2500, preferably 150-1500, preferably 200-750,preferably 250-500.

In one embodiment, the waste plastic pieces may comprise other polymericmaterials. Exemplary polymeric materials or plastic materials that maybe used in addition to, or in lieu of polyethylene include, but are notlimited to, polypropylene, polystyrene, polyvinyl chloride,polyvinylidene chloride, polyacrylonitrile, high impact polystyrene,acrylonitrile butadiene styrene, polyethylene/acrylonitrile butadienestyrene, polycarbonate/acrylonitrile butadiene styrene, acrylicpolymers, polybutadiene, polyisoprene, polyacetylene, silicones,synthetic rubbers and the like and copolymers and mixtures thereof. In apreferred embodiment, the waste plastic pieces are post-consumer waste.

In one embodiment, the waste plastic pieces have a specific gravity of0.80-1.20, preferably 0.85-1.10, more preferably 0.90-1.05, even morepreferably 0.92-1.02. However, in some embodiments, the waste plasticpieces may have a specific gravity of less than 0.80 or greater than1.20. Preferably, the waste plastic pieces have a water absorption ofless than 0.25%, preferably less than 0.10%, preferably less than 0.05%,preferably less than 0.01%.

In one embodiment, the waste plastic pieces have a surface roughness,Ra, of 1-50 μm, preferably 20-40 μm, however, in some embodiments, thesurface roughness may be greater than a Ra of 50 μm. In one embodiment,the waste plastic pieces have an RMS surface roughness of at least 100nm, preferably at least 500 nm, more preferably at least 1 μm. Suchsurface roughness properties may be determined by AFM.

In a related embodiment, the method further comprises reshaping thewaste plastic pieces by melting, extruding, and/or grinding. Forinstance, HDPE may be sourced from used or post-consumer products,including but not limited to milk jugs, detergent bottles, butter tubs,food containers, waste containers, drink bottles, and water pipes. Insome embodiments, the plastics may be sorted based on color, thickness,or other properties. These materials may be shredded, cleaned, melted,pressed, rolled, extruded, pelletized, or ground into other shapes thatmay be more easily transported to a plant for being formed into recycledproducts. In an alternative embodiment, an expanded waste plastic may beused, for instance, expanded PET or PS.

In one embodiment, the waste plastic pieces may be treated with UVirradiation, corona discharge, ozone, oxygen plasma, or with some otherprocess that changes the exterior surface of the waste plastic pieces.For instance, the treatment may increase a surface roughness and surfacearea by exfoliating or blistering, and the Ra or RMS surface roughnessmay increase by a factor of at least 1.1, preferably at least 1.4, morepreferably by a factor of 1.6. This increased surface roughness may thenincrease the compressive strength of the structural lightweightconcrete.

In a preferred embodiment of the invention, the waste plastic pieces aremixed with other solid components of the structural lightweightconcrete, such as the Portland cement, fine aggregate, and/or coarseaggregate (if other than plastic) prior to mixing with water. Firstmixing one or more of the solid components of the structural lightweightconcrete with the waste plastic particles forms a roughened or temperedwaste plastic particle having greater affinity for the solid componentspresent in the structural lightweight concrete. The waste plasticparticles (coarse aggregate) are preferably added to the concretemixture, in particular the Portland cement, separately from the fineaggregate and the water. In an even more preferred embodiment thePortland cement is heated to a temperature that is ±5° C. of the glasstransition temperature of the material from which the waste plasticparticles are made. Preferably, the temperature of the Portland cementpowder is at least 1° C. more than the glass transition temperature ofthe material from which the waste plastic particles are made. In caseswhere the waste plastic particles comprise more than one thermoplasticmaterial and the mixture of thermoplastic materials have different glasstransition points, the Portland cement is heated to a temperature of ±5°C. of the glass transition temperature of the waste plastic componentthat is present in the greatest amount with respect to the total amountof the waste plastic materials.

Mixing the waste plastic particles with a Portland cement powder at atemperature that is more than the glass transition temperature of thewaste plastic particles ensures good compatibility between the hydrationstructure that is formed when the hydraulic concrete composition iscured and the waste plastic particles. Mixing with Portland cement at atemperature greater than the glass transition temperature may embedPortland cement particles within the surface of the waste plasticparticles. Later curing with water results in a cured hydrationstructure that extends into the waste plastic particles to a depth atwhich the Portland cement particle is embedded in the waste plasticparticle. Alternately, Portland cement powder is better able tochemically modify the surface of the waste plastic particles when heatedto a temperature above the glass transition temperature of the materialfrom which the waste plastic particles are made. Chemical modificationmay include surface activation and bond formation between one or morePortland cement components and the waste plastic particle and/orcompositions obtained by sharing a hydraulic Portland cement component.

In one embodiment, and the waste plastic pieces have an average longestdimension of 1-12 mm, preferably 2-11 mm, more preferably 3-10 mm. Inone embodiment, the waste plastic pieces are in the form of granules,fibers, and/or flakes.

In one embodiment, the waste plastic pieces may be in the form ofgranules having a cylindrical shape. In one embodiment, the granules maybe reshaped from plastic by melting and extruding through a circulardie. The extruded plastic may be cut perpendicular to its length aftersolidification to form the cylindrically-shaped granules. An exampleembodiment of such granules is shown in FIG. 2A. In one embodiment, thegranules may have an average diameter of 1-4 mm, preferably 1.5-3 mm, orabout 2 mm, and an average length of 1-7 mm, preferably 1.5-6, morepreferably 2-5 mm. However, in some embodiments, the average diametermay be smaller than 1 mm or larger than 4 mm, or the average length maybe shorter than 1 mm or longer than 7 mm.

In one embodiment, the waste plastic pieces may be in the form offlakes, which may be obtained by grinding used plastic products. Oneembodiment of the flakes is shown in FIG. 2C, and another embodiment isshown in FIG. 2D. In general, the flakes are two dimensional, having asmall thickness as compared to other dimensions. The flakes may also beconsidered as platelets. The flakes may have an average thickness of0.3-0.8 mm, preferably 0.4-0.7 mm, and an average longest dimension of1-8 mm, preferably 1.5-7 mm, more preferably 2-6 mm. However, in someembodiments, the waste plastic pieces may be in the form of flakes withan average thickness of less than 0.3 mm or greater than 0.8 mm, or anaverage longest dimension of shorter than 1 mm or longer than 8 mm.

In one embodiment, the waste plastic pieces are in the form of fibers,which may be obtained by mechanical grinding. The fibers have anelongated axis, and may resemble the shape of rice grains. FIG. 2B showsan embodiment of waste plastic pieces in the form of fibers. In oneembodiment, the fibers having an average diameter of 0.2-0.8 mm,preferably 0.3-0.7 mm, more preferably 0.4-0.6 mm, or about 0.5 mm. Thefibers may have an average length of 2-12 mm, preferably 2.5-11.5 mm,more preferably 3-10 mm. However, in some embodiments, the fibers mayhave an average diameter of less than 0.2 mm or greater than 0.8 mm,and/or an average length of less than 2 mm or greater than 12 mm.

In other embodiments, waste plastic pieces may come in a variety ofdifferent shapes, such as strings, grains, bricks, rings, boxes, rods,balls, ellipsoids, spikes, drops, pillows, or some other shape. In oneembodiment, different shapes of waste plastic pieces may be mixed withone another. For instance, a coarse aggregate may comprise 75 wt %limestone aggregate and 25 wt % flake and granule waste plastic pieces,relative to a total weight of the coarse aggregate. The waste plasticpieces may comprise a mixture having a flake to granule mass ratio of1:10-10:1, preferably 1:5-5:1, more preferably 1:2-2:1.

In one embodiment, the waste plastic pieces may be regular in one ormore dimensions, for instance, having a monodisperse diameter or length.As defined here, being monodisperse in a dimension means having acoefficient of variation or relative standard deviation, expressed as apercentage and defined as the ratio of the particle dimension standarddeviation (σ) to the particle dimension mean (μ), multiplied by 100%, ofless than 25%, preferably less than 10%, preferably less than 8%,preferably less than 6%, preferably less than 5%.

However, in other embodiments, the waste plastic pieces may be irregularin one or more dimensions, for instance, having a polydisperse diameteror length. A polydisperse dimension refers to a having a coefficient ofvariation or relative standard deviation, expressed as a percentage anddefined as the ratio of the particle dimension standard deviation (σ) tothe particle dimension mean (μ), multiplied by 100%, of greater than50%, preferably more than 70%. In yet another embodiment, the wasteplastic pieces may be simultaneously monodisperse in one dimension andpolydisperse in another dimension.

In one embodiment, the coarse aggregate comprises waste plastic piecesand further comprises at least one selected from the group consisting oflimestone, perlite, and scoria, at a weight percentage of 1-90 wt %relative to a total weight of the coarse aggregate.

In one embodiment, the coarse aggregate comprises limestone. As usedherein, limestone refers to a sedimentary rock composed largely of theminerals calcite and aragonite, which are different crystal forms orpolymorphs of calcium carbonate (CaCO₃). In a preferred embodiment, thelimestone comprises at least 50 wt % calcium carbonate relative to thetotal weight of the calcium carbonate, preferably at least 55 wt %,preferably at least 60 wt %, preferably at least 70 wt %, preferably atleast 80 wt % relative to the total weight of the calcium carbonate andup to 20 wt % silicon dioxide relative to the total weight of thecalcium carbonate, preferably up to 18 wt %, preferably up to 16 wt %,preferably up to 12 wt %, preferably up to 10 wt % silicon dioxiderelative to the total weight of the calcium carbonate. In certainembodiments, the limestone may contain at least a few wt % of othermaterials including, but not limited to, quartz, feldspar, clayminerals, pyrite, siderite, chert and other minerals, preferably lessthan 2 wt %, preferably less than 1 wt %, preferably less than 0.5 wt %relative to the total weight of the calcium carbonate. In a preferredembodiment, the coarse aggregate comprises limestone with an averageparticle size in the range of 1-20 mm, preferably 5-20 mm, preferably5-15 mm, preferably 10-15 mm, preferably 11-14 mm, preferably 12-13 mm.In one embodiment, the specific gravity of the limestone may be2.10-2.90, preferably 2.30-2.80, more preferably 2.50-2.70. In oneembodiment, the water absorption of the limestone may be 0.1-4%,preferably 0.5-3%, more preferably 0.8-1.5%.

In one embodiment, the coarse aggregate comprises perlite. As usedherein, perlite refers to an amorphous volcanic glass that has arelatively high water content, typically formed by the hydration ofobsidian. It occurs naturally and has the unusual property of greatlyexpanding when heated sufficiently. The perlite of the presentdisclosure may refer to perlite or expanded perlite. Perlite softenswhen it reaches temperatures of 800-900° C. Water trapped in thestructure of the material vaporizes and escapes, and this causes theexpansion of the material to 7-16 times its original volume. In apreferred embodiment, the structural lightweight concrete of the presentdisclosure has a weight percentage of the coarse aggregate in the formof perlite ranging from 1-10% relative to the total weight of thecomposition, preferably 2-8%, preferably 3-7%, preferably 4-6% relativeto the total weight of the structural lightweight concrete. In apreferred embodiment, the coarse aggregate comprises perlite with anaverage particle size of 1-10 mm, preferably 1.5-8 mm, preferably 2-6mm, preferably 2.5-5 mm, preferably 3-4 mm. In a preferred embodiment,the coarse aggregate is perlite comprising 65-80 wt % SiO₂, preferably70-75 wt % SiO₂ relative to the total weight of the perlite, 10-18 wt %Al₂O₃, preferably 12-15 wt % Al₂O₃ relative to the total weight of theperlite, 2-5 wt % Na₂O, preferably 3-4 wt % Na₂O relative to the totalweight of the perlite, and 2-6 wt % K₂O, preferably 3-5 wt % K₂Orelative to the total weight of the perlite. In certain embodiments, theperlite comprises various elements including, but not limited tocalcium, iron, magnesium, and oxides thereof in less than 2 wt %relative to the total weight of the perlite, preferably less than 1 wt %relative to the total weight of the perlite.

In a preferred embodiment, the coarse aggregate comprises scoria. Asused herein, “scoria” or “cinder” refers to a highly vesicular (pittedwith many cavities or vesicles), dark colored volcanic rock that may ormay not contain crystals (phenocrysts). It is typically dark in color(generally dark brown, black or purplish red) and basaltic or andesiticin composition. Scoria is relatively low in density as a result of itsnumerous macroscopic ellipsoidal vesicles. The holes or vesicles formwhen gasses that were dissolved in the magma come out of solution as iterupts, creating bubbles in the molten rock, some of which are frozen inplace as the rock cools and solidifies. Scoria differs from pumice,another vesicular volcanic rock, in having larger vesicles and thickervesicle walls, and hence a higher density. In a preferred embodiment,the coarse aggregate comprises scoria with an average particle size of1-30 mm, preferably 2-25 mm, preferably 3-20 mm, preferably 4-15 mm,preferably 4-10 mm.

In certain embodiments, the coarse aggregate comprises mixtures of wasteplastic pieces, limestone, perlite, and scoria, mixtures of wasteplastic pieces, perlite, and scoria, mixtures of waste plastic pieces,limestone, and scoria, and mixtures of waste plastic pieces, limestone,and perlite. In certain embodiments, the coarse aggregate comprises30-80 wt % limestone relative to the total weight of the coarseaggregate, preferably 40-77 wt %, preferably 50-75 wt % limestonerelative to the total weight of the coarse aggregate. In certainembodiments, the coarse aggregate comprises 10-30 wt % limestonerelative to the total weight of the coarse aggregate. In certainembodiments, the coarse aggregate comprises 30-90 wt % scoria relativeto the total weight of the coarse aggregate, preferably 33-50 wt %,preferably 35-45 wt % scoria relative to the total weight of the coarseaggregate. In certain embodiments, the coarse aggregate comprise 10-25wt % perlite relative to the total weight of the coarse aggregate,preferably 11-22 wt %, preferably 15-20 wt % perlite relative to thetotal weight of the coarse aggregate.

It is equally envisaged that the structural lightweight concrete of thepresent disclosure may be adapted to comprise other coarse aggregates.Exemplary coarse aggregates that may be used in addition to, or in lieuof limestone, scoria, and/or perlite include, but are not limited to,pumice, shale, clays, slate, expanded clays, vermiculite, diatomite,schists, expanded schist, and the like, and mixtures thereof.

In one embodiment, the wet concrete slurry further comprises 0.1-2.0 wt%, preferably 0.1-1.0 wt %, more preferably 0.2-0.8 wt % of asuperplasticizer relative to a total weight of the wet concrete slurry.Chemical admixtures refer to materials in the form of powder or fluidsthat are added to the concrete to give it certain characteristics notobtainable with plain concrete mixes. In certain embodiments, admixturesmay be added to the concrete at the time of batching and/or mixing. Asused herein, a “superplasticizer” or “high range water reducer” refersto a type of chemical admixture used where a well-dispersed particlesuspension is required. These polymers are used as dispersants to avoidparticle segregation and to improve the flow characteristics ofsuspensions such as in concrete applications. As used herein, a“plasticizer” or “dispersant” is an additive that increases theplasticity or fluidity of a material. Plasticizers increase theworkability of “fresh” concrete, allowing it to be placed more easily,with less consolidating effort. A superplasticizer refers to a class ofplasticizers that have fewer deleterious effects and can be used toincrease workability more than is practical with traditionalplasticizers. The addition of a superplasticizer to concrete or mortarallows the reduction of the water content and water to cement ratio,while not affecting the workability of the mixture. This effectdrastically improves the performance of the hardening fresh paste, thestrength of concrete increases when the water to cement ratio decreases.Such treatment improves the strength and durability characteristics ofthe concrete and enables the production of self-consolidating concreteand high performance concrete.

In one embodiment, the superplasticizer is a polycarboxylate, such asfor example a polycarboxylate derivative with polyethylene oxide sidechains, preferably the superplasticizer is a polycarboxylate ether (PCE)superplasticizer, such as for example the commercially-available GLENIUM51®. Polycarboxylate ether-based superplasticizers allow a significantwater reduction at a relatively low dosage as a result of their chemicalstructure which enables good particle dispersion. Polycarboxylateether-based superplasticizers are composed of a methoxy-polyethyleneglycol copolymer (side chain) grafted with methacrylic acid copolymer(main chain). The carboxylate group (COO⁻Na⁺) dissociates in water,providing a negative charge along the polycarboxylate ether backbone.The polyethylene oxide (PEO or MPEG) group affords a non-uniformdistribution of the electron cloud, which gives a chemical polarity tothe side chains. The number and the length of side chains are flexibleparameters that are easy to change. When the side chains have a largeamount of ethylene oxide units, the high molar mass lowers the chargedensity of the polymer, which decreases performance in cementsuspensions. To balance both parameters, long side chain and high chargedensity, it is often necessary to keep the number of main chain unitsmuch higher than the number of side chain units. The negatively chargedpolycarboxylate ether backbone permits adsorption onto positivelycharged cations in a cement water system. The adsorption of the polymerand its COO⁻ groups changes the zeta potential of the suspended cementparticles yielding electrostatic repulsion forces and steric hindrance.

In one embodiment, other superplasticizers may be mixed in the wetcement slurry. Exemplary superplasticizers that may be used in additionto, or in lieu of a poly carboxylate ether based superplasticizerinclude, but are not limited to, alkyl citrates, sulfonated naphthalene,sulfonated alene, sulfonated melamine, lignosulfonates, calciumlignosulfonate, naphthalene lignosulfonate, poly naphthalene sulfonates,formaldehyde, sulfonated naphthalene formaldehyde condensate, acetoneformaldehyde condensate, poly melamine sulfonates, sulfonated melamineformaldehyde condensate, polycarbonate, other poly carboxylates, otherpoly carboxylate derivatives comprising polyethylene oxide side chains,and the like and mixtures thereof.

The wet concrete slurry of the present disclosure also comprises water.In one embodiment, the dry ingredients may be mixed with each otherbefore mixing with the water. Cement sets when mixed with water by wayof a complex series of chemical reactions. The different constituentsslowly crystallize and the interlocking of their crystals gives cementits strength. Carbon dioxide is slowly absorbed to convert thePortlandite (Ca(OH)₂) into soluble calcium carbonate. When water ismixed with cement, the product sets in a few hours and hardens over aperiod of weeks. These processes can vary widely depending on the mixused and the conditions of curing the product. After the initialsetting, immersion in warm water will speed up setting; in someembodiments gypsum may be added as an inhibitor to prevent flashsetting. In principle, the strength continues to rise slowly as long aswater is available for continued hydration, but concrete is usuallyallowed to dry out after a few weeks causing strength growth to stop. Inone embodiment, the wet concrete slurry has a weight percentage of waterranging from 5-12 wt % relative to the total weight of the slurry,preferably 6-11 wt %, more preferably 7-10 wt %. However, in someembodiments, the wet concrete slurry may comprise more than 12 wt %water.

In one embodiment, the wet cement slurry has a weight ratio of water tocement in the range of 0.33-0.8, preferably 0.33-0.75, preferably0.33-0.70, preferably 0.33-0.65, preferably 0.33-0.6, preferably0.33-0.55, preferably 0.35-0.50, preferably 0.375-0.45, or about 0.4 andis sufficient to affect curing of the cement. A lower water to cementratio yields a stronger, more durable concrete, whereas more water givesa freer flowing concrete with a higher slump. Impure water can be usedto make the concrete herein, but can cause problems when setting or incausing premature failure of the structure. In a preferred embodiment,the water of the structural lightweight concrete of the presentdisclosure is potable water. However, in an alternative embodiment, abrine or salt water may be used in place of the water.

Additionally, concrete production is time sensitive, and thorough mixingis essential for the production of uniform high quality concrete.Equipment and methods should be capable of effectively mixing concretematerials containing the largest specified aggregate to produce uniformmixtures. Exemplary equipment includes, but is not limited to concretedrum mixer, a volumetric concrete mixer, or simple concrete mixer. Thereis a wide variety of equipment for processing concrete from hand toolsto heavy industrial machinery. Whatever the equipment used the objectiveis to produce the desired material and ingredients must be properlymixed, placed, shaped and retained within the time constraints.

As used herein, “workability” refers to the ability of a fresh fluidconcrete mix to fill the form/mold properly, optionally with vibration.Workability depends on water content, aggregate (shape and sizedistribution), cementitious content and level of hydration, it can bemodified by the addition of a superplasticizer. Workability can bemeasured by the concrete slump test, a simplistic measure of theplasticity of a fresh batch of concrete following the ASTM C 143 or EN12350-2 test standards. In one embodiment, slump is measured by fillingan “Abram's cone” with a sample from a fresh batch of concrete. The coneis placed with the wide end down onto a level surface; it is then filledin three layers of equal volume, with each layer being tamped with asteel rod to consolidate the layer. When the cone is carefully liftedoff, the enclosed material slumps a certain amount due to gravity. Arelatively dry sample slumps less than a relatively wet sample.

In one embodiment, the superplasticizer is added at an amount to the wetcement slurry in order to maintain a slump of 50-150 mm, preferably75-125 mm, preferably about 100 mm. In certain embodiments, one or moreaggregates or a portion of one or more aggregates may be pre-wettedand/or saturated with water. In certain embodiments, a separate pastemixing method may be used where cement and water are mixed into a pastesuch as by a high speed shear type mixer before combining thesematerials with aggregates or additives, preferably at a water to cementratio of less than 0.45, preferably less than 0.4, preferably less than0.35. In certain embodiments, up to half the batch water may be added tothe solid ingredients and this premix may be blended with the remainingbatch water and superplasticizer in dosages to maintain optimal slump.

As used herein, casting refers to the process in which a fluid material(i.e. the concrete mixture) is poured into a mold, which contains ahollow cavity of the desired shape, and then allowed to solidify orcure. The solidified part is also known as a casting, which is ejected,demolded or broken out of the mold to complete the process. Concrete isprepared as a viscous fluid so that it may be poured into forms to givethe concrete its desired shape. There are many different ways in whichconcrete formwork can be prepared, such as slip forming and steel plateconstruction or factory setting in the manufacturing of precast concreteproducts.

In certain embodiments, the method may further comprise curingprocedures. Cement is hydraulic and water allows it to gain strength,curing allows calcium-silicate hydrate (C—S—H) to form. Hydration andhardening of concrete is critical in the first 3 days, in approximately4 weeks, typically over 90% of the final concrete strength is reached.During this period concrete must be kept under controlled temperatureand humid atmosphere. In a preferred embodiment, this is achieved byspraying or ponding the concrete surfaces with water. In a preferredembodiment, the cast concrete products are demolded after greater than 6hours, preferably greater than 12 hours, preferably greater than 24hours and submerged in a curing chamber (or water tank) maintaining atleast 50% humidity, preferably at least 75% humidity, preferably atleast 90% humidity, preferably at least 100% humidity for greater than 7days, preferably greater than 14 days, preferably greater than 28 days.In one embodiment, rather than submerging in a water tank, a demoldedconcrete may be covered with a wet cloth or wet burlap. In certainembodiments, the curing procedure may further comprise increases intemperature or pressure for intermittent periods of time depending onthe desired properties of the cast concrete product.

As a construction material, concrete may be cast in almost any shapedesired, and once hardened, can become a structural (load bearing)element. Concrete can be used in the construction of structural elementslike panels, beams, pavements, street furniture, or may make cast insitu concrete for building superstructures like navigation locks, largemat foundations, large breakwaters, roads and dams. These may besupplied with concrete mixed on site, or may be provided with “readymixed” concrete made at permanent mixing sites.

In one embodiment, the cast concrete product may be a concrete masonryunit. As used herein, a concrete masonry unit (CMU) also known as cinderblock, hollow block, concrete brick, concrete block, cement block,besser block, or breeze block refers to a large rectangular block usedin building construction. Concrete blocks may be produced with hollowcenters (cores) to reduce weight or improve insulation. The use ofblockwork allows structures to be built in the traditional masonry stylewith layers (or courses) of staggered blocks. Concrete blocks may comein many sizes, for example 350-450 mm by 180-220 mm by 100-200 mm.Concrete block cores are typically tapered so that the top surface ofthe block (as laid) has a greater surface area on which to spread amortar bed. Most concrete masonry units have two cores, but three andfour core units may also be produced. A core also allows for theinsertion of steel reinforcement, tying individual blocks together inthe assembly, aimed towards greatly increased strength. To hold thereinforcement in proper position and to bond the block to thereinforcement, the cores must be filled with grout (i.e. concrete). Avariety of specialized shapes of concrete masonry units exist to allowspecial construction features. U-shaped blocks or knockout blocks mayhave notches to allow the construction of bond beams or lintelassemblies. Blocks with a channel on the end or “jamb blocks” allowdoors to be secured to wall assemblies. Blocks with grooved ends permitthe construction of control joints allowing a filler to be anchoredbetween the block ends. Other features such as “bullnoses” may beincorporated. A wide variety of decorative profiles also exist.

Concrete blocks, when built in tandem with concrete columns and tiebeams and reinforced with rebar, are a very common building material forthe load bearing walls of buildings, in what is termed “concrete blockstructure” (CBS) construction. Houses typically employ a concretefoundation and slab with a concrete block wall on the perimeter. Largebuildings typically use large amounts of concrete block; for even largerbuildings, concrete blocks supplement steel I-beams. Concrete masonrycan be used as a structural element in addition to being used as anarchitectural element. Ungrouted, partially grouted, and fully groutedwalls are all feasible. Reinforcement bars can be used both verticallyand horizontally inside the concrete masonry unit to strengthen the walland result in better structural performance.

In certain embodiments, the structural lightweight concrete of thepresent disclosure may further comprise one or more additional chemicaladmixtures. Exemplary additional chemical admixtures include, but arenot limited to, accelerators, retarders, air entraining agents,pigments, corrosion inhibitors, bonding agents, pumping aids and thelike. Accelerators speed up the hydration (hardening) of concrete andmay be especially useful for modifying the properties of concrete incold weather. Exemplary accelerators include, but are not limited to,CaCl₂, Ca(NO₃)₂ and NaNO₃. Retarders, such as polyol retarders, slow thehydration of concrete and may be used in large or difficult pours wherepartial setting before the pour is complete is undesirable. Exemplaryretarders include, but are not limited to, sugar, sucrose, sodiumgluconate, glucose, citric acid, tartaric acid and the like. Airentraining agents (i.e. surfactants) add and entrain air bubbles in theconcrete, which reduces damage during freeze-thaw cycles, increasingdurability. Entrained air entails a reduction in strength and if toomuch air becomes trapped in the mixing defoamers may be used toencourage the agglomeration of air bubbles causing them to rise to thesurface and disperse. Pigments may be used to change the color of theconcrete, for aesthetics. Corrosion inhibitors may be used to minimizethe corrosion of metal (i.e. steel) that may be used as reinforcement inthe concrete. Bonding agents (typically a polymer) may be used to createa bond between old and new concrete with wide temperature tolerance andcorrosion resistance. Pumping aids improve pumpability, thicken thepaste and reduce separation and bleeding.

In certain embodiments, the structural lightweight concrete of thepresent disclosure may further comprise a viscosifying agent to modifythe rheological properties of the composition. Exemplary viscosifyingagents include, but are not limited to, cellulose ethers,polysaccharides, hydroxyalkylcelluloses, hydroxyethylcelluloses,methylcellulose, carboxymethylcellulose, hydroxyethylcellulose orethylhydroxyethylcellulose, polyethylene oxides, polyvinyl alcohols,polyamides and the like or mixtures thereof.

In certain embodiments, the structural lightweight concrete of thepresent disclosure may further comprise one or more additionalreinforcements. Concrete is strong in compression, as the aggregateefficiently carries the compression load. However, it is weak in tensionas the cement holding the aggregate in place can crack, allowing thestructure to fail. Reinforced concretes may add exemplary materialsincluding, but not limited to, steel reinforcing bars, steel fibers,glass fibers, carbon fibers, carbon nanofibers, plastic fibers and thelike or mixtures thereof to aid in carrying tensile loads.

In one embodiment, the structural lightweight concrete does not comprisefly ash. In one embodiment, the wet concrete slurry consists of onlyPortland cement, sand (fine aggregate), limestone (coarse aggregate),waste plastic pieces (coarse aggregate), and water. In a relatedembodiment, the wet concrete slurry consists of only Portland cement,sand, limestone, waste plastic pieces, water, and superplasticizer. In arelated embodiment, the wet concrete slurry consists of only Portlandcement, sand, waste plastic pieces, and water.

As used herein, compressive strength is the capacity of a material orstructure to withstand loads tending to reduce size, as opposed totensile strength, which withstands loads tending to elongate. In otherwords, compressive strength resists compression (being pushed together),whereas tensile strength resists tension (being pulled apart).Compressive strength can be measured by plotting applied force againstdeformation in a testing machine, such as a universal testing machine.Preferably, a concrete needs a compressive strength of at least 20 MPato be considered a structural concrete. In one embodiment, thestructural lightweight concrete of the present disclosure may have acompressive strength of 20-40 MPa, preferably 24-36 MPa, more preferably26-34 MPa. However, in some embodiments, the structural lightweightconcrete may have a compressive strength of less than 20 MPa, or greaterthan 40 MPa. In one embodiment, the structural lightweight concreteobtains the compressive strength as those mentioned previously when thewet concrete slurry is left to set or cure for 7-40 days, preferably14-30 days, however, in some embodiments, the compressive strengths maybe obtained in under 7 days or over 40 days of setting.

As used herein, thermal conductivity is the property of a material toconduct heat or alternatively the ability of a material to absorb heat.It can also be defined as the quantity of heat transmitted through aunit thickness of a material due to a unit temperature or the ratiobetween the heat flux and the temperature gradient. Heat transfer occursat a lower rate across materials of low thermal conductivity than acrossmaterials of high thermal conductivity. Correspondingly, materials ofhigh thermal conductivity are widely used in heat sink applications andmaterials of low thermal conductivity are used as thermal insulation.The SI units for thermal conductivity is measured in watts per meterKelvin (W/(m·K)). The conductivity of concrete depends on itscomposition. In a preferred embodiment, the structural lightweightconcrete of the present disclosure in any of its embodiments has athermal conductivity in the range of 0.50-1.10 W/(m·K), preferably0.52-1.02 W/(m·K), preferably 0.60-1.00 W/(m·K), preferably 0.65-0.95W/(m·K), preferably 0.67-0.93 W/(m·K), preferably 0.68-0.92 W/(m·K).However, in some embodiments, the thermal conductivity may be less than0.50 W/(m·K) or greater than 1.10 W/(m·K). In one embodiment, thestructural lightweight concrete obtains a thermal conductivity as thosementioned previously when the wet concrete slurry is left to set or curefor 7-40 days, preferably 14-30 days, however, in some embodiments, thethermal conductivity may be obtained in under 7 days or over 40 days ofsetting. In a preferred embodiment, the structural lightweight concreteof the present disclosure in any of its embodiments has a thermalconductivity that is up to 80% less than the thermal conductivity of anormal weight concrete composition, preferably up to 70%, preferably upto 60%, preferably up to 55%, preferably up to 50%, preferably up to45%, preferably up to 40% less than the thermal conductivity of a normalweight concrete composition. In one embodiment, the structurallightweight concrete may be considered a “thermal insulating concrete”due to its low thermal conductivity compared with a normal weightconcrete, which may have a thermal conductivity of about 1.7 W/(m·K). Astructural lightweight thermal insulating concrete may use theabbreviation SLWTIC. In one embodiment, the structural lightweightconcrete has both a compressive strength of 20-40 MPa and a thermalconductivity of 0.50-1.10 W/(m·K).

As used herein, unit weight (y, also known as specific weight) is theweight per unit volume of a material. The unit weight of structurallightweight concrete of the present disclosure will vary depending onthe composition of the aggregates and the unit weights of theconstituent aggregates. In a preferred embodiment, the structurallightweight concrete of the present disclosure in any of its embodimentshas a unit weight in the range of 1,400-2,000 kg/m³, preferably1,450-1,800 kg/m³, more preferably 1,500-1,700 kg/m³. However, in someembodiments, the unit weight may be lower than 1,400 kg/m³, or greaterthan 2,000 kg/m³. In one embodiment, the structural lightweight concreteobtains a unit weight as those mentioned previously when the wetconcrete slurry is left to set or cure for 7-40 days, preferably 14-30days, however, in some embodiments, the unit weight may be obtained inunder 7 days or over 40 days of setting.

The examples below are intended to further illustrate protocols forpreparing, characterizing and using the structural lightweight concrete,and are not intended to limit the scope of the claims.

Example 1

Materials and Evaluation

The developmental work was executed in three major stages. The firststage involved selection and acquisition of recycled plastics andchemical admixtures, and designing of trial mixtures. In the secondstage, mixture proportions for the properties of structural lightweightthermally insulated concrete (SLWTIC) were obtained by preparing severaltrial mixtures and measuring their strength and unit weight. In thethird phase, specimens were prepared from the mixture proportionsobtained from the trials in the second stage. The prepared specimenswere then tested to assess their mechanical and thermal properties.

The following materials were utilized in the preparation of SLWTICmixtures:

i. Portland cement

ii. Coarse aggregates (crushed limestone)

iii. Recycled plastic aggregates

iv. Fine aggregate (desert sand)

v. Superplasticizer

vi. Water

ASTM C 150 Type I cement with a specific gravity of 3.15 was utilized inall the mixtures. The chemical composition of the cement is shown inTable 1.

TABLE 1 Chemical composition of cement. Constituent Weight % SiO₂ 20.52Fe₂O₃ 3.8 Al₂O₃ 5.64 CaO 64.35 MgO 2.11 Na₂O 0.19 K₂O 0.36 SO₃ 2.1 Losson ignition 0.7 Alkalis (Na₂O + 0.658 K₂O) 0.43 C₃S 56.7 C₂S 16.05 C₃A8.52 C₄AF 11.56

Crushed limestone with a maximum size of 12.5 mm was used as coarseaggregate. The specific gravity of the coarse aggregate was 2.60 and thewater absorption was 1.1%. The physical properties of the limestoneaggregate are shown in Table 2, and the chemical composition is shown inTable 3.

TABLE 2 Physical properties of limestone aggregate. Property ValueSpecific gravity 2.6 Absorption (%) 1.1-1.4 Fineness Modulus 3.23 Unitweight (kg/m³) 1845 Material finer than 0.32% ASTM # 200 Sieve Loss onAbrasion 23.50% Clay lumps and 0.45% friable particles

TABLE 3 Chemical composition of limestone aggregate. Constituent Weight% CaO 54.97 SiO₂ 0.01 Al₂O₃ 0.17 Fe₂O₃ 0.05 SiO₂ + Al₂O₃ + Fe₂O₃ 0.23(>=70) MgO 0.64 Loss on ignition 43.66

Recycled plastic obtained from a plastic recycling plant was used ascoarse aggregate. The specific gravity of the recycled plasticaggregates was 0.95, and there was no water absorption.

The recycled plastic used in the disclosure is generally obtained byrecycling the plastics used in the packaging applications. The packagingmaterials are usually manufactured from polyethylene (LDPE or HDPE).Consequently, the composition of the waste plastic depends on the sourcematerial used. The shape and size of the used recycled plastic (granule,flake, or fiber) are generally controlled by the recycling process.

Based on their shapes, the plastic aggregates were classified asgranules, flakes, and fibers. FIGS. 2A-2D show the different types ofrecycled plastics used in this invention.

Recycled plastic granules were produced by chopping the extruded moltenwaste plastic after its solidification. The granules used in thedisclosure are cylindrical in shape with a diameter of about 2 mm and2-5 mm long.

Flakes were obtained from recycled waste plastic by mechanical grinding.They were of irregular size and shape, and predominantly two dimensionaland thin. The length and width were in the range of 2-6 mm.

Fibers were also obtained by mechanical grinding of waste plastic. Thediameter was about 0.5 mm and the length was in the range of 3 to 10 mm.

Desert sand with a specific gravity of 2.56 and water absorption of 0.6%was used as fine aggregate. The grading of fine aggregate is shown inTable 4.

TABLE 4 Grading of fine aggregate. ASTM Size opening Sieve # (mm) %passing 4 4.75 100 8 2.36 100 16 1.18 100 30 0.600 76 50 0.300 10 1000.0150 4

A superplasticizer (GLENIUM 51®) was added to the concrete mixtures toobtain the required slump of 100±25 mm. The dosage of thesuperplasticizer was between 0.4% to 1.6%, by weight of the cement. Theproperties of the superplasticizer are shown in Table 5.

Potable water was used in the preparation of all the mixtures and curingof the SLWTIC specimens.

TABLE 5 Technical data of superplasticizer (GLENIUM 51 ®). PropertyValue Appearance Brown liquid Specific gravity @ 20° C. 1.08 ± 0.02g/cm³ pH-value @ 20° C. 7.0 ± 1.0 Alkali content ≤5.0 Chloride content≤0.1%

Example 2

SLWTIC Mixtures

SLWTIC mixtures were prepared with a cement content of 350 or 370 kg/m³and a water/cement (w/c) ratio of 0.4 or 0.45. SLWTIC mixtures wereprepared with 25, 50, 75 or 100% recycled plastic aggregates by weightof total coarse aggregates in conjunction with conventional limestoneaggregates. Desert sand was used as the fine aggregate. The quantity ofsuperplasticizer was varied from 0.4% to 1.6%, by weight of cement, toobtain workable concrete mixtures.

The mixture constituents were mixed in a 0.7 m³ concrete drum mixer for2 to 3 minutes, and then about half of the water was added while thedrum was still rotating until all the particles were wet. The measuredquantity of the superplasticizer was added gradually to the remainingwater that was then added to the mix. Mixing was continued until auniform consistency was achieved. The mixed concrete was poured in moldsof different sizes and shapes that are required for determining themechanical properties and thermal properties of the developed SLWTIC.The filled molds were vibrated until a thin film of mortar appeared onthe surface of the specimens. The specimens were covered, after casting,with a plastic sheet and left for 24 hours in a laboratory environment(22±3° C.) to minimize the loss of mix water. After 24 hours, thespecimens were demolded and cured for 28 days by covering with wetburlap.

The descriptions and compositions of the concrete samples are shown inTables 6 and 7, respectively.

TABLE 6 Description of concrete samples by Mix #. Mix # Description M125% Recycled Plastic Granules and 75% Limestone-350-0.45 M2 25% RecycledPlastic Granules and 75% Limestone-370-0.40 M3 50% Recycled PlasticGranules and 50% Limestone-350-0.45 M4 50% Recycled Plastic Granules and50% Limestone-370-0.40 M5 75% Recycled Plastic Granules and 25%Limestone-350-0.45 M6 75% Recycled Plastic Granules and 25%Limestone-370-0.40 M7 100% Recycled Plastic Granules and 0%Limestone-350-0.45 M8 100% Recycled Plastic Granules and 0%Limestone-370-0.40 M9 25% Recycled Plastic Fibers and 75%Limestone-350-0.45 M10 25% Recycled Plastic Fibers and 75%Limestone-370-0.40 M11 50% Recycled Plastic Fibers and 50%Limestone-350-0.45 M12 50% Recycled Plastic Fibers and 50%Limestone-370-0.40 M13 25% Recycled Plastic Flakes and 75%Limestone-350-0.45 M14 25% Recycled Plastic Flakes and 75%Limestone-370-0.40 M15 50% Recycled Plastic Flakes and 50%Limestone-350-0.45 M16 50% Recycled Plastic Flakes and 50%Limestone-370-0.40 M17 75% Recycled Plastic Flakes and 25%Limestone-350-0.45 M18 75% Recycled Plastic Flakes and 25%Limestone-370-0.40 M19 100% Recycled Plastic Flakes and 0%Limestone-350-0.45 M20 100% Recycled Plastic Flakes and 0%Limestone-370-0.40

TABLE 7 Weight percentage composition of concrete samples. Coarseaggregates Total Lime Fine Super Mix Cement, Water, Stone, Plastic,Aggregates Plasticizer, # % % % % Sand, % % M1 16.4 7.9 22.6 7.5 45.30.2 M2 17.2 7.4 22.5 7.5 45.1 0.2 M3 18.2 8.6 14.6 14.6 43.8 0.2 M4 19.18.1 14.5 14.5 43.6 0.3 M5 19.9 9.3 7.1 21.2 42.3 0.3 M6 20.8 8.7 7.021.1 42.1 0.3 M7 21.4 9.9 0.0 27.3 41.0 0.3 M8 22.5 9.2 0.0 27.2 40.80.3 M9 16.4 7.9 22.6 7.5 45.3 0.2 M10 17.2 7.4 22.5 7.5 45.1 0.2 M1118.2 8.6 14.6 14.6 43.8 0.2 M12 19.1 8.1 14.5 14.5 43.6 0.3 M13 16.4 7.922.6 7.5 45.3 0.2 M14 17.2 7.4 22.5 7.5 45.1 0.2 M15 18.2 8.6 14.6 14.643.8 0.2 M16 19.1 8.1 14.5 14.5 43.6 0.3 M17 19.9 9.3 7.1 21.2 42.3 0.3M18 20.8 8.7 7.0 21.1 42.1 0.3 M19 21.4 9.9 0.0 27.3 41.0 0.3 M20 22.59.2 0.0 27.2 40.8 0.3

Example 3

Evaluation of Properties

The 28-day unit weight and compressive strength of the developed SLWTICwere measured on 100 mm×100 mm×100 mm cube specimens.

The compressive strength was determined according to ASTM C39 after 28days of curing. The load was applied at a rate of 3.0 kN/s until thefailure of the specimen and the compressive strength was obtained bydividing the failure load by the area of cross section of the specimen.

A total of 54 (50 mm diameter×20 mm thick) concrete cylindrical diskswere prepared to measure the thermal conductivity. A FOX 50 Heat FlowMeter was used for measuring the thermal conductivity according to ASTMC518 and ISO 8301. The FOX 50 provides rapid results in a compactfootprint. This equipment is an ideal choice for the measurement ofthermal conductivity of medium-conductivity materials, such as plastics,ceramics, glasses, composites, concrete, etc.

Three specimens from each mix were tested. Measurements were taken onboth faces of each specimen; thus, six readings were obtained for eachmixture, and the average of these readings was considered in theanalysis.

The properties of the developed SLWTICs are discussed in the followingexamples.

Example 4

Specimens with Granule-Shaped Recycled Plastic Aggregates

Following is a listing of the properties of SLWTIC prepared withgranule-shaped recycled plastic aggregates:

-   -   1. The unit weight was in the range of 1,497 kg/m³ to 2,049        kg/m³ as shown in FIG. 3. These values are within the specified        limits for structural lightweight concrete (SLWC).    -   2. The compressive strength of the developed SLWTIC varied from        16.27 MPa to 35.05 MPa, as shown in FIG. 4. A compressive        strength of more than 20 MPa was achieved in mixtures containing        25% and 50% of recycled plastic aggregates as the coarse        aggregate. Thus, these mixtures can be used as structural        concrete. However, mixtures with 75% and 100% recycled plastic        aggregates exhibiting compressive strength of less than 20 MPa        can be used as non-structural concrete.    -   3. The thermal conductivity of the developed SLWTIC was in the        range of 0.53 W/(m·K) to 1.09 W/(m·K) (FIG. 5), which is low        compared to the thermal conductivity of normal weight concrete        (NWC), which is 1.7 W/(m·K). This makes the developed SLWTIC a        highly desirable energy efficient material.

Example 5

Specimens with Fiber-Shaped Recycled Plastic Aggregates

Following is a listing of the properties of SLWTIC prepared withfiber-shaped recycled plastic aggregates:

-   -   1. The unit weight is in the range of 1,770 kg/m³ to 2,063        kg/m³, as shown in FIG. 6. These values are within the limits        specified for SLWC.    -   2. The compressive strength of the developed SLWTIC is in the        range of 14.90 MPa to 22.10 MPa, as shown in FIG. 7. A        compressive strength of more than 20 MPa was achieved with the        mixture containing 25% recycled plastic aggregates. Thus, this        mixture can be used as structural lightweight concrete. However,        mixture with 50% recycled plastic aggregates exhibiting a        compressive strength of less than 20 MPa can be used as        non-structural lightweight concrete.    -   3. The thermal conductivity of the developed SLWTIC was in the        range of 0.61 W/(m·K) to 1.07 W/(m·K) (FIG. 8), which is low        compared to the thermal conductivity of NWC which is 1.7        W/(m·K). This makes the developed SLWTIC a highly desirable        energy efficient material.

Example 6

Specimens with Flake-Shaped Recycled Plastic Aggregates

Following is a listing of the properties of SLWTIC prepared withflake-shaped recycled plastic aggregates:

-   -   1. The unit weight is in the range of 1,607 kg/m³ to 2,061        kg/m³, as shown in FIG. 9. This value is within the unit weight        requirements for SLWC.    -   2. The compressive strength of the developed SLWTIC is in the        range of 13.40 MPa to 28.40 MPa, as shown in FIG. 10. A        compressive strength of more than 20 MPa was achieved with        mixtures containing 25% and 50% of recycled plastic aggregates.        Thus, these mixture can be used as structural lightweight        concrete. However, mixtures with 75% recycled plastic        aggregates, exhibiting compressive strength of less than 20 MPa,        can be used as non-structural lightweight concrete.    -   3. The thermal conductivity of the developed SLWTIC was in the        range of 0.59 W/(m·K) to 1.0 W/(m·K) (FIG. 11), which is low        compared to the thermal conductivity of NWC which was measured        to be 1.7 W/(m·K). Thus, this material can be utilized for        thermal insulation purposes.        The Developed SLWTIC has the Following Attributes:    -   1. They can be used as a lightweight concrete since the unit        weight is less than 2,000 kg/m³.    -   2. Some of the mixtures can be used as structural lightweight        concrete since the compressive strength is more than 20 MPa.    -   3. Mixtures with low compressive strength can be used as        non-structural lightweight concrete.    -   4. The thermal conductivity of the developed concrete is much        less than that of the normal weight concrete. Thus, it can be        used as a thermal insulating material.

Concrete specimens prepared with different percentages of recycledplastic aggregates, as partial replacement of natural limestoneaggregates, have exhibited very low unit weight, adequate compressivestrength, and low thermal conductivity. Thus, some of the developedSLWTIC mixtures can be utilized as structural lightweight concrete whileothers can be utilized as non-structural lightweight concrete. All thedeveloped mixtures have exhibited high thermal resistance. The highthermal insulation of the developed SLWTIC will lead to a significantsaving in energy required for air conditioning in hot weather conditionsand heating in cold regions. Also, the use of recycled plastic inconcrete will result in environmental benefits by solving problemsassociated with the safe disposal of non-biodegradable waste plastic.

The invention claimed is:
 1. A method of recycling a waste polyolefinand making a structural lightweight concrete, the method comprising:extruding the waste polyolefin and chopping the extruded wastepolyolefin to form waste plastic pieces having a cylindrical shape witha diameter of about 2 mm and 2-5 mm long; mixing: 12-25 wt % Portlandcement; 37-57 wt % fine aggregate; 5-40 wt % coarse aggregate; and 5-12wt % water to form a wet concrete slurry, wherein each weight percentageis relative to a total weight of the wet concrete slurry; and curing thewet concrete slurry to produce the structural lightweight concrete,wherein the fine aggregate is sand with an average particle size of0.3-1.5 mm, wherein the coarse aggregate comprises: at least 10 wt %waste plastic pieces having an average longest dimension of 1-12 mm, and1-90 wt % of at least one selected from the group consisting oflimestone, perlite, and scoria, wherein each weight percentage isrelative to a total weight of the coarse aggregate, wherein thelimestone has an average particle size in a range of 1-20 mm, whereinthe perlite has an average particle size in a range of 1-10 mm, whereinthe scoria has an average particle size in a range of 1-30 mm, andwherein the structural lightweight concrete has a compressive strengthof 20-40 MPa, a thermal conductivity of 0.50-1.10 W/(m·K), and a unitweight of 1,400-2,000 kg/m³.
 2. The method of claim 1, wherein the wasteplastic pieces have a specific gravity of 0.80-1.20.
 3. The method ofclaim 1, wherein the waste plastic pieces have a surface roughness Ra of1-50 μm.
 4. The method of claim 1, wherein the waste plastic piecescomprise 20-100 wt % polyethylene, relative to a total weight of theweight plastic pieces.
 5. The method of claim 1, wherein the wet slurryfurther comprises a polycarboxylate ether superplasticizer.
 6. Themethod of claim 1, wherein the wet concrete slurry has a slump of 50-150mm.
 7. The method of claim 1, wherein the Portland cement is an ASTM C150 cement selected from the group consisting of Type I, Type Ia, TypeII, Type IIa, Type II(MH), Type II(MH)a, Type III, Type IIIa, and TypeIV.
 8. The method of claim 1, wherein limestone is present, having anaverage particle size of 5-20 mm.